Tests
1st tests to order
serum creatinine and blood urea nitrogen (BUN)
Test
All patients diagnosed with AIN have an elevated serum creatinine BUN. Rise in serum creatinine may be acute or subacute.[1]
Result
elevated
CBC with WBC differential
urinalysis
Test
Sterile pyuria (leukocyturia with a negative bacterial urine culture) is often present.[1]
The absence of dysmorphic red blood cells (RBCs) and RBC casts excludes acute glomerulonephritis.
Heavy proteinuria is seen with concurrent nephrotic syndrome.
Result
sterile pyuria; low-grade proteinuria; WBC casts
trial of discontinuing triggering medication
Test
Symptoms may resolve following discontinuation of the triggering medication; a retrospective diagnosis of AIN can be made if this occurs.
Result
resolution of acute kidney injury
antineutrophil cytoplasmic antibody (ANCA)
Test
Performed if associated systemic disease suspected.
Result
positive result suggestive of systemic vasculitis
antinuclear antibody (ANA)
Test
Performed if associated systemic disease suspected.
Result
positive result consistent with systemic lupus erythematosus
anti-double stranded DNA (anti-ds DNA)
Test
Performed if associated systemic disease suspected.
Result
positive result consistent with systemic lupus erythematosus
complement profile
Test
Performed if associated systemic disease suspected.
Result
low C3/C4 levels consistent with complement-activating glomerulonephritis (such as systemic lupus erythematosus or postinfectious glomerulonephritis)
Tests to consider
kidney ultrasound
Test
Shows large, swollen kidneys that are often echogenic due to the inflammatory interstitial infiltrates.
Main use is to exclude hydronephrosis, renal calculi, or shrunken kidneys (a sign of chronic renal failure).
Result
large, swollen, echogenic kidneys
kidney biopsy
Test
Only test that provides a definitive diagnosis.
Also provides information on severity of disease, clues to possible etiology, and prognosis.
Performed in patients who have not responded to discontinuation of the triggering medication, where diagnosis is unclear, or if corticosteroid treatment is being considered.[11]
If nephrotic syndrome is present, the pattern is usually minimal change disease, although membranous nephropathy has also been reported.
Requires a careful risk-benefit assessment in consultation with a nephrologist.
Result
interstitial inflammatory infiltrate with variable numbers of eosinophils, lymphocytes, and plasma cells; infiltration of inflammatory cells into tubules (tubulitis)
kidney gallium scan
Test
Findings are nonspecific.
May be useful when negative to exclude a diagnosis of AIN when kidney biopsy is not an option.[26]
Result
interstitial lesions
urine cytokines
Test
Urine interleukin-9 and tumor necrosis factor-alpha may help differentiate AIN from other causes of acute kidney injury.[27]
Result
elevated urinary tumor necrosis factor-alpha and interleukin-9
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